Fuel can be more completely combusted within a cylinder of an internal combustion engine by creating a more homogeneous mixture of fuel and fresh air. Inducing swirling motion, i.e. swirl, of fresh air within an engine cylinder can promote more homogeneous mixing, particularly when fuel is injected directly into the engine cylinder before the onset of combustion.
A known construction for imparting swirl to intake flow as the flow enters an engine cylinder through an open intake valve comprises a swirl-inducing structure in an intake port of the engine cylinder upstream of the intake valve. The presence of such a structure however contributes to restriction of the intake flow, and such restriction may have one or more various side effects on combustion and/or engine performance.
Certain engines comprise multiple intake valves for a single engine cylinder. In the absence of any swirl-inducing structure, the presence of multiple intake valves is generally ineffective in imparting in-cylinder swirl to intake flow entering an engine cylinder. The presence of certain swirl inducing structures may be effective to impart some swirl.